The invention relates to an adjustable-length tool holder for a rotating tool.
Conventional tool holders for rotating tools, for example drills, milling cutters or reaming tools, as have been disclosed, for example, by U.S. Pat. No. 5,311,654, have a base element which is provided with a coupling shank for connecting to a machine tool and which, axially remote from the coupling shank, ends in a sleeve part forming a central locating opening. The coupling shank may be a conventional standard connection, for example in the form of a steep-angle taper or the like. The sleeve part accommodates the shank of the tool in an interference fit and can be thermally widened by means of a heating device, preferably an inductive heating device, so that the tool shank, firmly seated in the sleeve part in the cooled state, can be axially inserted into or removed from the locating opening of the sleeve part.
Furthermore, it is known from U.S. Pat. No. 5,311,654 to design the tool holder in two pieces. A tubular-cylindrical reducing sleeve is shrunk into position in the locating opening of the base element, this reducing sleeve in turn forming a locating opening for the tool shank. The reducing sleeve also accommodates the tool shank in an interference fit and projects beyond the sleeve part of the base element with its region which transmits the interference-fit forces, so that the reducing sleeve, irrespective of whether or not it is inserted into the base element, can be widened thermally, for example by means of the induction heating device, in order to change the tool.
The locating opening of both the sleeve part and the reducing sleeve extends over the entire axial length of the tool holder and is provided with a plurality of grooves, for example 4 grooves, in the inner lateral-surface region which transmits the interference-fit forces to the tool shank, via which grooves cooling fluid can be fed through the tool holder to the tool during operation of the latter.
In practice, it is desirable to have adjustable-length tool holders, in particular in the form of the heat-shrinkable tool holders explained above. In conventional heat-shrinkable tool holders, although the tool shank can be axially positioned in many cases, there are comparatively strict limits to this possibility due to the fact that the dimensions of the tool holder are always fixed. The object of the invention is to specify a heat-shrinkable tool holder which enables the tool to be selectively positioned relative to the coupling shank within very wide limits without impairing the torque-transmitting properties of the tool holder.
To achieve this object, an adjustable-length tool holder for a rotating tool is proposed according to the invention, this adjustable-length tool holder comprising:
a base element, which is provided with a coupling shank for connecting to a machine tool and which, axially remote from the coupling shank, ends in a sleeve part forming a central locating opening, and a plurality of tubular-cylindrical extension sleeves which in turn each form a central locating opening and of which a first extension sleeve is arranged in an interference fit in the locating opening of the sleeve part in such a way that it can be positioned in an axially variable manner, and each of the further extension sleeves is arranged in an interference fit in the locating opening of the adjacent extension sleeve toward the base element in such a way that it can be positioned in an axially variable manner, the tool being arranged with its shank in an interference fit in the locating opening of the extension sleeve located furthest away from the base element, and it being possible for that region of the sleeve part and of each of the extension sleeves which transmits the interference-fit forces to be widened by heating, in particular by means of an induction heating device, for the insertion or positioning or removal of the extension sleeve or of the tool shank.
In such a tool holder, the extension sleeves are telescopic relative to one another and to the sleeve part of the base element, so that the axial length of the tool holder overall can be varied within very wide limits. The surfaces participating in the transmission of the interference-fit forces and assigned to one another can be produced in a highly precise manner, so that precise concentricity properties are achieved despite variable positioning. The outside diameters of the extension sleeves expediently correspond to standard diameters of tool shanks, so that the number of extension sleeves used for the extension can be selected in accordance with the practical requirements, and, if need be, with a set of extension sleeves stepped in outside diameter or/and inside diameter, not only can the axial length of the tool holder be varied, but the tool holder can also be adapted to the nominal diameter of the tool shank ultimately to be clamped.
In a preferred configuration, provision is made for that region of the sleeve part and of the extension sleeves which transmits the interference-fit forces to in each case reach essentially up to the front end axially remote from the coupling shank, and for the locating opening of the sleeve part or/and of the extension sleeves to be extended beyond the region which transmits the interference-fit forces axially toward the coupling shank and to be enlarged in diameter relative to the diameter of the region which transmits the interference-fit forces. Since the region which transmits the interference-fit forces reaches up to the axial front end, the tool holder has improved torque-transmitting properties. The region which transmits the interference-fit forces has a defined axial length, preferably about 2 to 3 times the diameter of the locating opening, a factor which facilitates the thermal widening, since it can remain limited to the defined region. Nonetheless, the telescopic length of each extension sleeve and of the sleeve part may be selected to be considerably larger, since the region accommodating the telescopic excess length is enlarged in diameter. The axial length of that region of the locating opening of at least the extension sleeves which is enlarged in diameter is expediently at least 1.5 times, preferably at least 2 times, the axial length of the region which transmits the interference-fit forces.
In a preferred configuration, provision is made for a plurality of axially elongated slots which are distributed in the peripheral direction of the locating opening and which are open toward the locating opening but do not pass radially completely through the extension sleeve to start from that end of the region of at least the extension sleeve of smallest diameter which is axially remote from the coupling shank, this region transmitting the interference-fit forces. If they are present in sufficient number, slots of this type increase the effective diameter for the shrink-fitting expansion in the region which transmits the interference-fit forces relative to the inside diameter of the locating opening and thus reduce the requirements for maintaining production tolerances. This is especially important in the case of small inside diameters if seizing problems are to be avoided when shrinking the tool shank or possibly the extension sleeves in position. The slots are incorporated in the extension sleeve, which is otherwise closed in a ring shape. Each of the extension sleeves or/and the sleeve part are provided with such slots increasing the effective diameter for the shrink-fitting expansion.
The slots preferably start essentially directly at the front end axially remote from the coupling shank and extend in the axial direction expediently over at least 5-10 mm, since the shrink-on problems are greatest here, but preferably at least over the length of that region of the locating opening which transmits the interference-fit forces and may, if need be, have a radial depth which changes in the axial direction, in particular a radial depth decreasing from the insertion side of the tool shank toward the coupling shank.
In order to reduce the contact surface of the locating opening as little as possible, this contact surface transmitting the torque, the width of the slots in the peripheral direction is as small as possible. The slots expediently have a width of between 0.1 mm and 0.5 mm in the peripheral direction. In order to be able to produce them in a simple manner despite the small width, the slots have essentially parallel slot walls.
The radial depth of the slots determines the increase in the diameter, effective for the thermal expansion, of the region which transmits the interference-fit forces. The radial depth is dimensioned in such a way that an effective expansion diameter is obtained which enables the locating opening to be produced with sufficiently large tolerances, which are thus simple to realize. Since the effective expansion diameter of the sleeve part is to be all the greater, the smaller the nominal diameter of the locating opening is, provision is made in a preferred configuration for the radial depth of the slots in that region of the locating opening which transmits interference-fit forces, at a nominal diameter of the locating opening of less than or equal to 10 mm, to be greater than 0.1 times the nominal diameter, preferably equal to or greater than 0.2 times the nominal diameter. In this case, the nominal diameter is the value of the outside diameter of the element accommodated in the region which transmits interference-fit forces. At a nominal diameter of the locating opening of less than or equal to 6 mm, the radial depth of the slots is preferably greater than 0.15 times the nominal diameter, but better equal to or greater than 0.3 times the nominal diameter, and, at a nominal diameter of the locating opening of less than or equal to 3 mm, the radial depth is expediently greater than 0.2 times the nominal diameter, but preferably equal to or greater than 0.5 times the nominal diameter. These dimensions ensure that the web regions of the sleeve part which remain between the slots are still sufficiently flexurally rigid during torque loading.
The number of slots arranged in the peripheral direction preferably at equal angular distances is to be a compromise between, on the one hand, sufficient bearing capacity of the web regions remaining between the slots and, on the other hand, the improvement in the expansion behavior of the extension sleeve. At least 6 slots, but better at least 8 slots, are expediently provided. In order not to excessively reduce the contact surface effective during the torque transmission, at least 20 slots are expediently provided.
The radially outer bases of the slots preferably lie on the lateral-surface contour of a cone having a cone apex axially facing the coupling shaft. This also facilitates the production of relatively narrow slots, for example by the electrical-discharge wire cutting process.